The present invention relates to a seat reclining mechanism for vehicles, and more particularly to a seat reclining mechanism for supporting a seat back in such a manner as to freely adjust an inclination angle of the seat back with respect to a seat cushion.
A conventional seat reclining mechanism has been for example shown in the Japanese Patent Laid-Open Publication No. 2-128707 (1990). This has a lower arm held to a seat cushion frame, an upper arm rotatably supported to the lower arm and held to a seat back frame, a rotational shaft rotatably supported to the lower arm and inserted into a hole formed on the upper arm so as to provide a rotation center of the upper arm with respect to the lower arm, a lock mechanism comprising a ratchet and a plurality of pawls which are arranged in a space between the lower arm and the upper arm and adapted to be engaged with each other so as to restrict a rotation of the upper arm with respect to the lower arm when the upper arm is to be secured to the lower arm, and a cam supported to the rotation shaft in such a manner as to be integrally rotated and press an inner surface of the pawls so as to engage the pawls with the ratchet.
Further, in this conventional mechanism, a diameter of a through hole of the cam to which the rotation shaft is inserted is greater than a diameter of the rotation shaft, and the cam freely move with respect to the rotation shaft in a radial direction, so that the pawls are certainly pressed so as to engage all the pawls with the ratchet due to a movement of the cam with respect to the rotation shaft in a radial direction.
However, in the former conventional mechanism mentioned above, although a certain engagement between all the pawls and the ratchet is secured by adjusting the position of the cam with respect to the pawls, the pressing force of the cam to the pawls tends to be relatively low due to this adjustment, so that there is a fear that all the pawls are not always firmly engaged with the ratchet. Accordingly, there has been a fear that a backlash in a rotating direction is generated in an engagement between the pawls and the ratchet, and there has been also a fear that a rotation restriction of the upper arm with respect to the lower arm by the lock mechanism is insufficient.